The Future of Human Evolution.

Great Debates
1

I’ve run across (and at times contributed to) a few threads that have touched upon this theme, but they have been mainly thread <hijacks>. From what I gather, many Dopers take the position that human biological evolution will progress full steam ahead, perhaps even transmogrifying us into a new species. My position is quite the opposite. Thinking this to be an interesting question in it’s own right, I’m promoting it to the head of the thread as an OP.

While some species go multi-millions of years virtually biologically unchanged (e.g. crocodilians), and others seem to be evolving right before our eyes (e.g. bacterial resistance), evolution for most species, I suspect, progresses at a rate somewhere in between. Let’s consider the evolution of Homo sapiens. Indeed, we’ve done our fair share of evolving over the last few billion years – we didn’t pop out of the primordial ooze clicking iPod navigation wheels with opposable thumbs, after all. But, from this point forward, how will human biological evolution progress? Will it be more crocodilian or more bacterial in nature?

Expanded Question:
Biologically speaking, to what degree will Homo sapiens evolve in the next 1,000,000+ years?

Ground rule assumptions:

  1. Our species will not self-annihilate and no future human endeavor (e.g. war, genetically engineered virulence etc.) will result in a global mortality rate greater than 25%.
  2. The next 1,000,000+ years on earth will progress similarly to the last 1,000,000+ years with regard to geological, climatic and cosmological events. IOW: We will continue to experience plate tectonics, periodic Ice ages, small to medium sized astral-planetary impacts etc., but we will experience no major catastrophic event –types likely to result in mass extinctions (i.e. runaway greenhouse effect, large planetary impacts).
  3. We may assume that extra-planetary colonization will be a future reality, but for this discussion we will limit our analysis to the core non-emigrant human population. (Alien crossbreeding is likewise prohibited).
  4. The focus of this thread is on biological evolution - traits that are passed on through succeeding generations - unaltered by technological intervention. Biotechnology and genetic engineering will, of course, evolve to a high degree in the future, but their debate inclusion, while interesting and welcome, should be kept as an aside to the question of pure biology.

Please choose one of the following choices and argue your position:
A) We will not evolve at all: (self-explanatory).
B) We will evolve minimally: (e.g. atavistic organs, immunological shifts etc).
C) We will evolve moderately: (e.g. Readily apparent morphological changes like enlarged craniums, extra extremities etc.).
D) We will evolve into a new species: (self-explanatory).

My choice is “B”. I’ll type and post my position shortly.

2

We will evolve in such a way as to optimize our reproductive fitness. Whatever genetic traits are now found in humans which promote reproductive fitness will become more common. Any such traits which are already common will remain common. Whatever genetic traits are now found in humans which decrease reproductive fitness will become less common, and any such traits which are already uncommon will remain so. Some new traits will probably crop up; these traits will either become more common or dwindle away according to whether they promote or inhibit reproduction. The environment will change in a variety of ways, and as a result, some traits which were previously detrimental will become advantageous, and vice-versa.

Yes, that’s all extremely vague. A fuller answer would require a listing of some of the genetic traits in humans which promote or hinder reproduction. The problem is that many human traits are cultural, not genetic, and cultural evolution can occur so much faster than genetic evolution that it’s difficult to discern the genetic components. Consider, for instance, a person who is disposed to choose not to have sex. This is certainly a trait which hinders reproduction, and if it were genetic, it would be selected against. But is it genetic? That’s very difficult to say.

Or another example: Wilt Chamberlain slept with thousands of women in his life, and probably ended up siring hundreds of children as a result. Clearly, the Stilt was very reproductively fit. But how much of his fitness was genetic? His fitness was doubtless due at least in part to his athletic ability, and at least some of that was surely genetic. But how much? And whatever traits he had that women liked, did they like it because of their own genetic predispositions, or because of cultural acclimation? It’s conceivable that in a generation or two, athletes will be out of style, and nerds will be the sexy fad (well, OK, so that’s largely wishful thinking). If that’s the case, then Wilt’s many decendants won’t be at any particular advantage, even if they did inherit his athletic aptitude.

3

Another problem with speculation on future evolution is that there’s no way to know what conditions our descendants will be faced with. Evolution can (and will) cause many different variations in future humans if the species survives long enough, but not all of them will be successful.

4

One dramatic factor to take into account is the fact that humans have and will continue to take an active role in guiding their own evolution, including direct modification of the genome. We’ve been consciously guiding the evolution of domestic animals for millenia via selective breeding; although it is (currently) morally repugnant to consider doing the same to human beings, in the end the benefits of gene selection and modification will most likely win out.

Given that, I think it’s pretty much impossible to talk about the specifics of future human evolution, other than to say that the results will be unimaginably different from anything produced by nature. I find it not entirely unlikely that we may differentiate into distinct species based upon general function, not entirely unlike scenerios predicted by Wells and Huxley. Many may agitate against this on bioethics grounds, but in the end, the approach that is most effective for propagating the species will benefit the parties who elect to engage in it.

Stranger

5

The problem with not including this, is I think it will almost certainly become the dominant force in human biology. Not to mention, it’s likely at the same time to largely stall natural evolution, as natural mutations will simply be deleted.

However, assuming this is somehow prevented, I’d vote for D. With any real technology, there’s to much interbreeding and migration for a seperate population to last long enough to speciate. on the other hand, with that much time, I’d expect minor changes to add up.

6

I think the contraints that the OP has placed on the possible future outcomes are so completely unrealistic as to make the original question meaningless. Essentially you are asking how we will evolved if the major forces that cause evolution are ignored.

But the reality is that genetic engineering will likely turn us into something entirely different if we’re still around in 1M years. We’ll probably have dozens of species and subspecies that are incapable of breeding with each other naturally. But that won’t matter either, since we’ll have the technology to breed those populations together in the lab.

7

You all must forgive me, but this example, to support the significance of reproductive fitness in evolution, and to put up “the Stilt” as an example of reproductive fitness, has me rolling all over the floor. Chronos, I’ve always regarded your posts exhibiting above average education and intelligence, but you must be getting bored.

Please allow me to pick this post apart:

  1. I’ll accept that Wilt may be as old as me or older, but I doubt very much that he has had as many ejaculations as I’ve had. Jerking off takes way more energy than copulation.
        Given the stereotype of the sexual successes of black NBA players and the ongoing debate on whether or not their athletic prowess is due to genetics, I find the connection of reproductive fitness with genetics hilarious.

There is evidence of only three children. Big deal, I have only two, but I’ve taken precautions all the other times.

Wilt certainly has attributes of sexual attraction that are superior to mine. His ability to elicit the desire of a woman to prostrate herself and receive his semen has a 1000 times higher potential for success than I experienced. Big deal. I have the “American dream”. Today, whether or not, to have a child is ultimately a woman’s choice, and who the father is involves far more complicated and relevant criteria than sexual fitness.

To answer the OP

My biggest fear for future generations is the rising cost of medical care because nature’s method of discontinuing genetic fuckups, even minor ones, is increasingly is being thwarted by advanced medicine. Universal health care could implode. However, if the science permits and society can overcome its reticence towards abortion, both legal and moral, we stand a fighting chance to keep the human species healthy.

I hate myself for even suggesting this, but it has to be said.

8

One thing that people don’t understand is that the selective pressure against rare deleterious recessive traits is very very small, likely very close to the mutation rate that produces the trait. And this is even for traits that are very very likely to kill the victim before they reproduce.

But how can that be? For common deleterious recessive traits, the selection pressure is very large. Or it would be, if there were very many common deleterious recessives, which there aren’t, because the selective pressure on them is so high. Make sense?

Now, consider a genetic disease, Lemur’s Syndrome. Caused by a recessive gene, it has 100% fatality rate by age 1. Let’s pretend the number of live births is 1 million per year (ease of calculation), and there are 25 cases of Lemur’s syndrome every year. So 1 person in 2,500 exhibits the trait, and all these children die. But…how common is the trait? The incidence is 0.000025. Pretty rare trait, right? Except, if we assume mating is random (that is, people who are carriers of the trait aren’t more likely than chance to mate with each other), then 1 in 100 people are carriers. 0.01 times 0.01 equals 0.0001, and since only 1/4 of the offspring of two carriers will have the disease, the incidence if 1 in 100 is a carrier is .000025. If the population is (say) 250,000,000 people, then we have 2.5 million people who are carriers, but we only saw 25 individuals selected out by exhibiting the disease.

If we suddenly had a cure for Lemur’s Syndrome would the incidence of Lemur’s syndrome skyrocket, becuase all those kids with bad genes are now going to grow up to reproduce? Not at all, because now instead of 2,500,000 people with the trait we now have 2,500,025 people with the trait, although they should count double since they have two copies, so 2,500,050. A miniscule change in the incidence of the gene, a rounding error.

MOST people carry several deleterious recessive traits of this type. You can’t clean up the gene pool and get rid of deleterious genetic traits by killing, or sterilizing the people who exhibit the trait, because most of the people with the gene for the trait don’t exhibit the trait. And the rarer the genetic disease is, the ratio of people who have the trait to people who are carriers for the trait gets smaller and smaller.

Now, the trouble comes when the odds of carrier mating with another carrier is NOT random. Like tight-knit communities that discourage marrying outside the community, or geographically isolated communities, or incest. And if a couple has a baby with the disease, each new child they have has a 1 in 4 chance of also having the disease.

So we’re not going to purge genetic diseases from the population just by tough-mindedness, abortion, euthanazia, and sterilization, even if you sterilize the entire family of a child who exhibits the disease, because the vast majority of carriers never have a child who exhibits the disease because they are very unlikly to mate with another carrier. You’d have to kill the MAJORITY of the population to get rid of most rare genetic diseases because there are dozens of rare genetic disease like my fictional example of Lemur’s syndrome.

So evolutionary degeneration caused by allowing the genetically impure to remain alive through medical intervention is a non-issue, it isn’t even going to increase the incidence of children with a treatable form of the disease except by a trifling amount. You’d do much better reminding people not to marry their cousins if a genetic disease runs in their family.

9

I just finished reading a book called visions, the author is a well known physicist.

http://www.amazon.com/gp/product/0385484992/104-0213338-9620711?v=glance&n=283155

The author wrote it in the early 90s and alot of the stuff he predicted about IT and the internet came true. I don’t know if that makes him an expert about the future though.

In his eyes human evolution is over. Waiting tens of thousands of years for mild genetic variations will not happen because technology is alot faster and because human mating partners are so wide and varied that all you get is genetic drift, you don’t get the entire species traveling in one direction.

In his eyes there are 3 levels of civilization; 1, 2 & 3. Each civilization requires about 10 billion times the power as the preceding civilization. Level 1 is a global civilization with a global government that relies on earth to provide all it’s energy. Level 2 is a solar civilization. Level 3 is a galactic civilization. He feels we are a level 0 who are a few hundred years away from being a level 1 civilization.

It is hard to tell because there is no telling what we’ll figure out in the future. I would assume within 200 years we’ll know enough about proteomics and genetics to do almost whatever we want with our bodies and evolution though. But who knows where that will take us.

10

Women that are resistant or unresponsive to hormonal birth control will become more common.

11

Why? Sure, on the surface, this seems intuitive… but it’s also pretty Lamarckian. You’re suggesting that humans will change in direction X (evolve resistance) to solve problem Y (overcome birth control). That is as ridiculous as suggesting a giraffe will evolve a long neck to reach upper foliage.

Imagine the real-life scenario. Let’s say individual A has indeed mutated to become resistant to whatever form of birth control pill she is using. Let’s say, then, that she becomes pregnant. Assuming she has the baby (which can’t be assumed, given she didn’t want a baby in the first place) and assuming she passes on that particular mutation, what exactly is the force that is selecting for that trait? That is, what gives someone with that mutation a selective advantage over someone without that mutation?

That is the problem with this whole thread, and any “scientist” that proposes any hypothesis regarding the evolution of humans in the future. They assume evolution is directional.

12

I have to agree. What evolution happens in the future on the human genome will be very hard to track, because we are very close to fooling with out own genes outright, and we already have a hard time distinguishing the biological from the social.

13

The fact that she’s more likely to produce a baby despite being on that kind of birth control, compare to a woman who lacks that mutation. Of course, that assumes that she won’t just switch methods, or it won’t become obsolete.

14

The birth control one is easy to answer, although it requires a couple of assumptions.

2 women take birth control pills. One is not resistant, and does not become pregnant. One is resistant, the birth control pills don’t work, and she becomes pregnant. If these were the only two women in the population, and resistance to birth control were entirely hereditary, and there were no other forms of birth control, then the next generation would be entirely composed of women who are resistant to birth control pills. The normal gene is selected against, the resistant gene is selected for.

Of course, many women aren’t going to take birth control pills, there are other forms of birth control, resistance to birth control might not be entirely genetic, women might get abortions rather than carry unplanned pregnancies to term, birth control pills could improve such that the resistant gene offers no protection, genetic engineering could make it all moot, such a mutation must actually exist in the first place, it must be common enough that genetic drift doesn’t drive the allele to extinction, etc, etc.

But it seems likely that since birth control pills don’t work for all women, and it seems likely that some of that variation is genetic, there will probably be some increase in the number of women who are resistant to birth control pills…IF birth control pills in their current form continue to be used for many more generations. As long as women who are resistant to birth control have slightly more children on average than women who aren’t, the proportion of women who are resistant will increase every generation.

15

Exactly. But how does this higher fecundity of resistant females come about? Doesn’t seem likely, given that they are trying to prevent birth. But you seem to know that, anyway.

There is no reason to expect such an outcome, which was my problem with the statement and others like it.

16

It comes about because, for a variety of reasons (religious, moral, hormonal, legal), women who are on the pill and get pregnant sometimes have the baby. Women who are on the pill and don’t get pregnant can’t have the baby.

17

I get that part. But we’re not talking about bacteria becoming resistant to an antibiotic. There isn’t strong enough selection for this trait to assume it will become more prevalent.

18

As long as it’s consistent for long enough, even a tiny selection bias can cause a trait to evolve. The problem isn’t the size of the selection pressure, it’s that human societies aren’t generally unchanging enough for long enough for them to have an effect.

19

But if there’s ANY selection for the trait it will become more prevalent, unless random factors (genetic drift) overwhelms selection and drives the allele to extinction before it can become common enough. Even a selective bias of 1% will make a huge difference over many generations.

Yes, of course we’d have to use birth control pills as an important method of birth control for several hundred years for this effect to be noticable. That still doesn’t mean it wouldn’t happen.

20

As noted in my OP, my choice is “B”. (humans will evolve minimally in 1-million years).

Let me align my position with a few mechanisms of evolution:

Adaptation:
In our not-too-distant past, humans crossed a watershed mark: from adapting themselves to the environment to adapting the environment to themselves. IMO, this renders adaptation, as a mechanism of biological evolution, virtually directionless.

Gene Flow:
As geographical and cultural barriers continue to erode, genes flow more freely. As species go, humans exhibit a high degree of heterogeneity (only dogs and perhaps a few other domesticated species exhibit more variability), but, as our specie matures, the trend certainly seems to be toward homogeneity. We’re becoming mongrelized. Our mutt-people progeny, though prosaic, will no doubt be genetically fit…and they will fetch well. We are converging as a species, not diverging.

Genetic Drift:
IMO, genetic drift in our large, increasingly homogenous, mobile population makes the fixation of mutated alleles impotent.

Mutation:
My guess is that the rate of copying error mutations will remain stable, while the rate of exposure-type mutations (i.e. radiation, chemical) will rise in our increasingly polluted environment. However, more mutations in toto does not necessarily translate into more or greater change. In this regard, the more important variable is the degree to which alleles become fixated, as opposed to being diluted to oblivion. Most mutated genes rumble around for a bit, and then disappear before finding permanent expression in progeny. Are human mutated genes likely to become fixated? I don’t think that they are, at least not to a large degree. I believe that both neutral mutations, because they are affected by gene drift and flow, and non-neutral mutations, because they are affected by natural selection, will tend not to become fixed in the general population.

Natural Selection:
>>A) Ecological Selection: The concept of survival of the fittest is not relevant to our species any more. The genetic make-up of people who survive and reproduce today is broad and heterogeneous - weak and strong alike pass their alleles into future generations. Sociology, hard science and technology will increasingly negate the drive of ecological selection. Technology adapts; biology doesn’t need to.
>>B) Sexual Selection: I believe that contemporary human sexual selection is, and will continue to be, the major impediment to evolutionary change for our species. Sexual drive may be instinctual for all species, but mate selection is not necessarily so, at least not for the most sapient of species – H. sapiens. We choose mates by free will, logic and emotions…and sometimes coercion. I posit the following:
Increased sapience = increased free will mate selection = decreased directed allele fixation = evolutionary homeostasis.
Human breeding crosses all borders (i.e. geographic, ethnic, cultural). Nearly every expressed human trait is attractive to someone and therefore likely to be bred and passed into future generations: fat/skinny, short/tall, aggressive/passive, smart/dumb…if it walks on two legs, someone will nail it (on second thought, even bipedalism isn’t a prerequisite for some). As opposed to instinctual sexual selection, which is predictable and positively directed, free will sexual selection is random and virtually directionless. Break-out, species-altering traits are unlikely to fixate in this chaotic brew of genetic stew.